Reversible electrochemical cells, i.e., secondary cells, storage batteries, and accumulators, are characterized in that the chemical relationships of the electrodes and the electrolyte may be restored to a condition of substantially full charge by causing current to flow into the cell. Exemplary of such cells are lead acid cells, nickel-iron-caustic soda cells, and nickel cadmium cells.
One class of secondary cells are cells having zinc halogen electrolytes. Zinc halogen cells are described, for example, in the article by Heise, Schumacher and Cahoon, A Heavy Duty Chlorine-Depolarized Cell, Journal of the Electrochemical Society, August, 1948, page 99, and in the article by Barnartt and Forejt, Bromine-Zinc Secondary Cells, Journal of the Electrochemical Society, Nov. 1964, page 1201. While zinc-halogen secondary cells have a high theoretical energy density and are capable of delivering high current at sustained voltages, they suffer from low voltage efficiency, i.e., a low value of the quotient of voltage during discharge divided by the average voltage during the corresponding charge.